The function of a differential in a vehicle is to adjust (accommodate) for different speeds between driven wheels, and also to maintain total motive force; that is, ensure an even (or otherwise desired) torque distribution over all driven wheels. This is necessary because when cornering in a vehicle, the outer wheels have a greater distance to travel compared to the inner wheels. Driving rear axles for goods vehicles are normally equipped with a differential lock that allows the vehicle drive shafts to be coupled together. When the differential lock is engaged thereby causing a blocking of the action of the differential between the driving wheels, the driving wheels are controlled to rotate at the same speed; that is to say, without equal torque distribution and producing a condition that increases wheel (tire) adhesion when the underlying surface is smooth and slippery. The differential between two driving wheels (in a pair of driving wheels) will henceforward be referred to as the wheel differential.
On vehicles equipped with two or more driving wheel pairs (that is to say four-wheel drive, six-wheel drive, and the like), differentials with differential locks may be arranged between such paired driving wheels. The differential between a two driving wheel pair will henceforward be referred to as the axle differential.
When one or more differential locks are activated for axle or wheel differentials, there is a risk of an unequal distribution of the torque between the drive shafts in a driving wheel pair or between respective driving wheel pairs. In the event of high positive or negative torques from the engine of the vehicle and high transmission ratios between the engine and the driving wheels (that is to say, when low gear is selected), drive shafts, differentials and their constituent components may be overloaded if the torque distribution is too unequal. Many drivers of goods vehicles know that it is necessary to exercise caution when increasing the torque in certain situations. Inexperienced drivers, however, run the risk of expensive damage to axle and differential components.
Known solutions include driver training courses and the use of driver manuals which both have as a goal to assure that driver can handle the vehicle correctly. Another solution is to equip these certain prone vehicles with an over-dimensioned shafts and/or differentials which can be quite expensive.
There is therefore a need to eliminate the risk of damage to the vehicle drive train (for example, rear axles, differentials, propshafts, wheel suspension etc.) when activating differential locks. This is the prime object of the invention described below.